The long term objective of this research is to determine how coordinated programs of gene expression direct development in eukaryotes. We are presently concentrating on a descriptive analysis of the coordinated gene sets active in Drosophila larval salivary glands which respond to the steroid hormone 20-hydroxyecdysone. We have used recombinant DNA techniques to isolate cloned genomic DNA segments which represent one model gene in the "intermolt" gene set (20-hydroxyecdysone represses) and several model genes in the "late" gene set. We plan to describe the tissue and temporal specificity of the intermolt gene located cytologically at 90BC on the polytene chromosome map. We will also assess the protein coding capacity of the abundant transcript which accumulates in the salivary gland and screen wild-type Drosophila stocks for transcriptional variants. We are initiating studies aimed at describing the clustered nature of the transcribed genes located in the "late" polytene puff 71CE. Similar temporal and tissue specificity descriptions of these genes are also planned. Lastly we will attempt to identify cloned DNA segments which represent the members of the "early" ecdysone-induced gene set by means of a differential hybridization screen.